Yosh build part deux

[first timer]

Here are a few pics as promised

[first timer]

[Nessism]

That things going to sound like a whistle parade going down the road. You sure you want to do that?

[first timer]

i doubt i am going to hear it over my strairght cut gears, lumpy cams, and race exhaust.

[posplayr]

I know it is Yoshi and nostalgic but it sure doesn't seem to make a whole lot of sense from an engineering perspective.

If to a first approximation convective heat flow is proportional to surface area avaliable, you have traded two time the area of the OD for 1 times the circumference times the fin thickness.

I wont do the calcs but I'm sure you loose.
Second, is there really any kind of an improvement in the air flow? At 60-100 mph I cant say you are going to see any incremental change is air flow. It is mostly due to the forward velocity.

So while it might be considered cool, somethings are best left in the past. This seems to be an overheating desperation move before using oil coolers.

Just my perception, if you have your heart set on drilling, have at it. I did the same on a rear rotor recently

[rapidray]

Just so you know, back in the day of the 1000cc Super bikes, all that drilling was done for one purpose, & one purpose ONLY - to reduce WEIGHT!!! You are building a street bike, not restoring a Yosh RACE bike. You need the cooling capability of the fins & ALL of their surface area. Ray.

[posplayr]

Ray,

Whoda thunk .

Tanks

Pos

[first timer]

i figured the gun kote, and the large earls cooler would be providing the cooling i need. Just reread the CW artical where they dig into the yosh engine and they state that the holes were drilled for cooling, all those holes i drilled i bet i only removed maybe a 1/4lb of material, hardly worth the effort to do only for weight reduction. The artical states to increase air turbulance to help with cooling. Even suzuki drilled six 1/2" holes in their 1100 cylinder block to help with cooling. So I can't be that far off base. Plus it's the head that has the most heat and I am hardly drilling that so most of the surface area should remain intacked. Maybe i'll step down a few of the holes from 1/2" to 3/8".

I am not to worried about heat, Craig Smith has been racing these motors 1200cc's at 12:1 with bunches of holes drilled into them (he was going for mostly looks too) and basic engine enamel no gun kote and hasn't had a heat issue.



If i am putting this much effort to get this bike looking and running like a race bike, over looking the holes wouldn't be real true to form. This bike is a little more then a street bike, I plan to do a few local vintage races with it at some point.

[salty_monk]

I was about to mention your oil cooler... If you like the look go for it I don't see why it would cause any real problems.

Dan

[posplayr]

I am not to worried about heat, Craig Smith has been racing these motors 1200cc's at 12:1 with bunches of holes drilled into them (he was going for mostly looks too) and basic engine enamel no gun kote and hasn't had a heat issue.

Now that I see the back side of that motor, if there is heat trapped behind the carbs, then maybe it will help. Go with what works.

I might mention that on the Yoshi GSXR's they have a heat sheild they put between the engine and carbs to keep heat off of the carbs and cool the air charge which is being directed in through norkles and hoses. It is oil cooled, but if ther wa a lot of heat build up you would think.......

Hey what is with the numbers on the pistons?

[first timer]

the engine with the #'s is Craig Smiths 1200cc 8v motor, he is from new zealand they do things diffrent down there

I am basing some of my hole locations on his motor.

[first timer]

so here is a fun little exercise in math, (Jim this one is for you!)

here's a little table showing how much loss or gain in surface area can be achieved by drilling the fins.


To be noted a 1/2mm in any direction (height or dia) can really throw the numbers into a differant direction.

So basically if i went with 3/8 holes i would be comitting to a 19% loss in cooling from the material removed. Which is not to be confused with total effieceny loss in cooling of the entire motor. To calculate that I would need to know the surface area of the engine........ But basically it would be a lot less then 19% when you comapare the surface area being removed from the availabe surface area of the fins, ( i think anyways math is not my strong point and it's late here )

Ok back to actully doing work instead of playing on the computer.

[posplayr]

so here is a fun little exercise in math, (Jim this one is for you!)

here's a little table showing how much loss or gain in surface area can be achieved by drilling the fins.


To be noted a 1/2mm in any direction (height or dia) can really throw the numbers into a differant direction.

So basically if i went with 3/8 holes i would be comitting to a 19% loss in cooling from the material removed. Which is not to be confused with total effieceny loss in cooling of the entire motor. To calculate that I would need to know the surface area of the engine........ But basically it would be a lot less then 19% when you comapare the surface area being removed from the availabe surface area of the fins, ( i think anyways math is not my strong point and it's late here )

Ok back to actully doing work instead of playing on the computer.

Ryan,
I got close to the same answer, you must have truncated PI to only 3 significant digits .

So at 4mm if you drill 5/16" holes there is no loss in surface area
if the thickness is 3mm then it drops to less than 1/4". Bu then there is a loss in cooling efficency due to teh holes being too small.

I think you should do what ever Yoshi did and be happy with the replica, that is the point right?

Jim

[first timer]

yeah i think i will mix it up with 3/8 holes and 1/2 holes, probably use mostly 3/8 holes, at least see what it looks like, you can always go bigger right just not the smaller

[gs road racer]

quote

"I am going to replace my guides with bronze ones, found some from Kibble White, what do you guys think? Anyone else you like? "

Unless they're worn (not likely) stay with stock. This kind of setup wears very well as opposed to the 4 valve motor with tappets that impart some sides forces. Or you want to go to smaller stem sizes as Pops did back then.I had spoken with APE about that and they'd have to be custom valves gets a bit expensive.. although in 80 you could get a bike for $10k in todays dollars $50k+....all relative.

What I have found in my yosh motor was top end oiling problems the cam journals scored badly as did the head. I think the 750 gears which spin the pump 30% faster would be a good choice and they'll be in my next build.